This study is designed 1) to determine the hormonal requirements for the induction and maintenance of the decidual reaction in human endometrium in vitro and 2) to further investigate the mechanisms by which estrogen and progesterone control the differentiation of stromal fibroblasts into epitheloid decidual cells. Endometrium will be obtained following biopsy or hysterectomy during ovulatory menstrual cycles. Pregnancy dendometrium (decidua) and throphoblast will be obtained after therapeutic abortion performed during the first trimester of normal gestation. Samples of endometrium will be incubated as tissue cultures or dissociated into epithelial and stromal components. Tissue explants and stromal cells (undifferentiated fibroblasts from proliferative and secretory endometrium, pre-decidual cells from late-secretory endometrium and decidual cells from pregnancy endometrium) will be cultured in serum-free nutrient medium with or without steroid hormones. In some experiments stromal cells will be co-cultured with epithelial elements (glandual and luminal epithelium) or trophoblast. The histologic appearance (morphologic criteria) and the amount of decidua prolactin (dPRL) produced (biochemical criteria) by these preaprations will provide an index of the extent to which estradiol and progesterone affect the decidual reaction in vitro.